Process for producing aviation gasoline



Oct. 28, 1947.A c. T. HARDING l PROCESS FOR PRODUC-ING AVIATION GASOLINE 2 Sheets-Sheet 1 Filed July 9, 1945 Oct. 2,8, 1947. c. T.IHARD|NG l* 2,429,71`8,

PROCESS FOR PRODUCING AVIATION GSOLINEv Patented Oct. 28, 1947 PROCESS Fon PRODUCING AVIATION v GASOLINE Clarke T. Harding, Hillside, N. J., assignor to Standard Oil Developm ration of Delaware ent Company, a corpo- Application July 9, v'1943, rSerial No. 494,000

. This invention relates to treatment-of hydrocarbons to` produce internal combustion engine' fuels,.and more particularly, relates to the pro'- duction of aviation gasoline.- Y y Modern aviation engines require fuels of high rich mixture performance in order to permit take-'off from the groundY when the airplane is heavilyloa'ded, or in other situations kwhere large powerjoutputs are needed. y Among other requirements', the aviation' fuel must have the proper distillation range, the proper-octane number obtained by thev conventional ASTM "measuring methods and high rich mixture performance measured as reference IMEP (indicated mean effective pressure in pounds per square inch) on aj standardr supercharged aviation gasoline test engine. This method 'is known as Aviation Fuels Division-C-Rich Mixture Octane Number meth-Y odk (AFD-SC-Rich Mixture) and also complies withArmy-Navy Specification method AN-VVA- There Vare two waysin which the'3C rich mixturerating'of an unknown fuel may be expressed; (1) as the equivalent vof a reference fuel S plus the cc.` of tetraethyl lead requiredV per gallon to be added to the reference fuelS to match the knock intensity ofthe unknown fuel (as, for ex- 7 Claims. (CL 196-12) East Texas heavyrn'aphthaatv 1400 F. Vis 316, thisV ample, YSel-2.5 cc.) developed on a stan-dard supery chargedaviation gasoline test engine; or (2) the referenceIMEP (indicated mean effective pressure in pounds Aper square inch) registered in the test engine at the specied intensity of knocking where the comparison against reference fuel S was made. i

The IMEPis then thevmaximum pressure capa` ble of being developed in the'test engine by the fuel being tested withoutpdetonation and is accordingly a measure of thev power output attainable with the given fuel. The higher the IMEP, the higher the power output of a given fuel or material and the more desirable the fuel or material/is. The IMEP of Sy fuel without lead, for example, is 168, with 2 cc. of lead itis 218, and withr obtain'a match in knocking tendency on the test engine. The unknown fuel is then rated as the equivalent of referencefuelrplus the lccQof lead or vS-l-X `where X is the number of vadditional cc. of lead. The second use above given o fmeasuring' rich mixture performance constitutes an alternative methodof expressing the identical test results and consists of measuring the indicated mean effective pressure registered in the explosionvcylinderof the test engine at the point of matching-knock againstthe reference fuel. v Y

If the unknown fuel is poorer than iso-octane -orthe reference ueLfthenfth-e reference fuel is diluted with alower octane number reference fuel (equivalent to by volume of 2,2,4-trimethyl pentaneand 5% by volume of n-heptane) called M until a match in knocking tendency is obtained yandtheV extent kfof dilution is. recorded as the rating of the unknown fuel.

Accordingly, it will be seen that blending age'antsy which possess IMEP blending values of 200 and above are very desirable provided their otherv properties conform to specifications. The IMEPs of benzene andtoluene,rfor`example, are aboutV 320 to 350, and the IMEP of thetotal aromatic cut (M5-350 F. boiling range) from cracking sobutane andjethylene`is,about320.` The isomer of 2,3-dimethyl butane, Y(l2-,dimethyl'butaneor neohexane) is not vnearly as potent, having an IMEP of only '220.f Since the severe U. S. Army specifications limit the amount `of aromatics which can be used in aviationlgasoline, it is evi-` dent Vthat isopara'nic'matrialsare of special interest, particularly for the highest performance Y aviation fuels.

According toi my invention, hydrocarbons are cracked andi then separatedinto differentfrac-l tions and'selected fractions are further treated and/or combinedto produce aviation gasoline together with some Shy-products. For example,`

`crude oils, gas oils, Vvirgin motor gasolines, etc.,

maybe usedas feed stocksbut'I prefer to `use heavy virgin naphtha as'the feedstock.

According to the-preferredform of my inven-f tion, heavy vir'gin'naphtha is severely cracked to." "convert substantially all the -paraiiins and naphthenes into relatively pure aromatics contaminated with olens and diolefns.- During this aromatics form an excellent blending material or base stock for aviation gasoline. rlhe ethylene is alkylated with isobutane produced from normal butane from an extraneous source and results in the production of large amounts of 2,3-dimethyl butane, which has a high IMEP and forms an excellent blending agent for aviation gasoline.

C3 hydrocarbons are also separated and alkylated with isobutane to form alkylate for use in the aviation gasoline.

If desired, a portion of the benzene may be separated and alkylated with propylene to form cumene which is suitable as a blending agent for the aviation gasoline.

From the cracked products butadiene is also separated, and if desired, it is possible to recover isoprene, piperylene, cyclopentadiene, and Various other diolenic or olenic materials. These materials are Well known as being valuable raw material for synthetic rubber or plastics.

In another form of the invention, motor gasoline' is used as the .feed stock and the gasoline is separated into a plurality of fractions by superfractienaton.- ISQheptape .and sopentane are recovered and directly introduced into the aviation gasoline. The C4 `fraction is separated into an isobutane and norma1 butane fraction, the isobutane being usedin the'alkylation zones and the normal buien@ being Passed te isomerastion zoneiforthe production of additional isobu'tane'. In this'form of theinvention, extraneous butane is also used and isomeriaecl to produce isobutane for the process;-

C5 and Ce hydrocarbons are isomerized in the presence of hydrogen and an isomerizing catalyst to produce higher boilingY branched chain hydrocarbons which are added directly to the aviation gasoline,

The higher boiling fractions of the motor gasoline are then severelyv cracked as above pointed out in connection with the heavy naphtha feed to produce aromatics and ethylene and other olens,

In the drawings.

Figl 1 represents an apparatus for carrying out the preferred form ofrny invention; and

Fig. 2 represents a portion of the apparatus for carrying "out a modification o f'my invention.

Referring now to the drawingkthe reference character II)` designates a line through which the feed is passed. The feed is preferably East Texas heavy virgin naphtha having a boiling range of about 200."4 to 410 F. The heavy naphtha feedl is passed through a conversion or cracking none I2 in a heater. I4.. Preferably, aV diluent gas is introduced through line I6 into the hydrocarbons passing to the cracking zone. Any suitable heated inert gas may be used, such as normally gaseous hydrocarbons, nitrogen, etc.,`but preferably superheated steam is used. The steam is used in an amount of about 86 mol per cent. The stock to be cracked contains mostly paraiiins and naphthenes, and` in'order to transform these into aromatic compounds and olens and diolefins, it has been found that the, feed. stock should be heated to aY temperature between about 1200 F. and 1400" F. for a relativelyl short period of time between about lOseconds and-Oil second, the longer times being usedwith theA lower temperatures. For example, when operating at a temperature of about 1400o F., the timev of,A contactA or reaction is about 0.2 second,

This severe heating andl cracking is especially adapted for my process because it produces aromatics boilingintheraviation gasoline range s ub- 1 Stantially free of lu ridesired parail'ins and atthe 4 same time produces large amounts of ethylene which is separated and mixed with isobutane and alkylated to form 2,3-dimethyl butane which has a high IMEP and forms a valuable aviation blending material. In addition, butadiene, isoprene, piperylene, cyclopentadiene, etc., are formed during the severe cracking and may be recovered as such.

After the cracking step, the products of reaction are quickly quenched by a quenching medium introduced through line I8 to a temperature of about 600-1000 F. to stop the reaction. The cooled reaction products are passed through line V22 to al fractionating tower 24 having a heating means 26. Water is removed in any suitable manner. The lighter hydrocarbons pass overhead through line 28 and are passed into a fractionating tower 32 referred to as a de-ethanizer. Tower 32 is provided with heating means 34. Bottoms from the fractionating tower 24 are withdrawn through line 36 and contain tar and fuel oil. The lighter products formed during the reaction contain gaseous products Which are separated in any suitable manner.

In the fractionatine tower 32 a pressure of about 500 lbs/sd. in. is maintained and ethylene is taken overhead through line 38 together with some ethane, methane, and hydrogen. The separated ethylene cut is preferably mixed with isobutane passing through line 42 and the mixture alkylated in the alkylation zone 44 to produce 2,3-dimethyl butane, as will be presently described in greater detail. Alternatively,A it is desirable in certain instances to use a more concentrated ethylene stream for alkylation, in which case one more fractionating'tower is added to separate methane and lighter from the whole stream prior to entering the de-ethanizer.

Bottoms from the fractionating tower 32l are passed through line 48 and introduced into a seco-nd fractionating tower 52 for removing propylene from the remaining constituents. The

tower 52 is maintained under aA pressure of about,

300 lbs/sq. in. The tower 52 is provided with a heating means 54. The propylene fraction is taken overhead through line 56 and is preferably mixed with the isobutane from line 58 and passed through line 62 to a seco-nd alkylation zone 64 for alkylating C3 and C4 hydrocarbonsv to be described in greater detail hereinafter. Bottoms from the tower 52 are passed through line 66 to a debutanizer tower 6,8. provided with a heating means '12.

The C4 fraction containing butane, isobutane,I butylenes and butadiene passes overhead through line 14. The C4 fraction is introduced into an extraction zone 16 where it is, mixed with a selective solvent for butadiene, such as aqueous ammoniacal copper solution,- more specifically an ammoniacal cuprous acetate solution.

The butadiene is recovered by solution and subsequent regeneration from the copper solution, and withdrawn through line 'I8 and the remaining portion of the C4 fraction is passed through line 82 to the alkylation zone 64. The alkylation treatment willbe described hereinafter in greater detail. y

Returning now to thebottoms from the debutanizer tower 68, the bottoms are withdrawnV through line 86 and treated with sulfuric acid having a concentration of aboutl 90.-98.% to remove olens and diolens from the desired cracked products which consist essentially of aromatic compounds. in the gasoline boiling range.

In order to minimize acidV degradation or for thealg-429,218;

to treating. Acid in the amount vof 25 lbs/bbl. of cracked products'may-be introduced into the treating z one 88 through line 92 and acid sludge maybe withdrawn through line `94. The drastic cracking treatment of the hydrocarbons passing through the cracking zone' l2 produces a preponderance of aromatics boiling in the aviation gasoline range, contaminated to a small extent with olens and diolefins, land by the acid treatment the olens and diolens are removed so that only aromatic compounds, such as toluene, benzene and xylene, and Ahigher aromatics remain as a pure aromatic fraction.

VThe acid-'treated products are washed with water and alkaline liquid Vin conventional manner and pass through line I 02 to a fractionating tower |04 provided with a heating means |06 to separate lighter aromaticcompounds from heavier aromatic compounds. The lighter fraction passes overhead through line` |68 and contains benzene, toluene and xylenes,4 the benzene and toluene forming about 75% by 'volume of the mixture. The toluene may be recovered from the mixture by fractionation and ,comprises nitration grade toluene without further treatment. About 99}% pure benzene may be recovered from the aromatic fraction by distillationV and kwithout further treatment.'

lThese pure aromatic compounds present in the aromatic fraction described may be put to Whatever use is most economic, such as nitration or alkylation, but form an extremely desirable constituent of aviation gasoline without separation or further treatment. [The higher' boiling aromatics up toY about 350 F. are also 'of excellent through line 38. The isobutane is produced from extraneous normal butane passing through line |28 to an'isomerization zone'r |22 at reaction temperature and is contactedwith a suitable isomerization catalyst to produce isobutane. The

. products of isomerization pass through line |24 to a fractionating zone |26 provided with a heating means 28to'separate isobutane frOm higher boiling constituents. Bottoms, including C5 and higher boiling hydrocarbons, are withdrawn through line |32`and introduced intofractionator |44 through line |33 for recovey of C5 and Cs materialsV or may pass through line I0 for severe cracking treatment in the cracking zone r| 2. Normal butane is withdrawn through line |34 and recycled through line |20 to the isomerization zone |22. AIsobutane is removed overhead through line |36 and a portion of this isobutane is passed through line 42 to the ethylene alkylation zone 44k and another portion of the' isobutane is passed through line 58 to the second alkylation zone 64.

Inthe simplest case,theethylene and isobutane areheated toa temperature of about 10G-130 F. and contacted with a suitable alkylation catalyst, such as aluminum chloride'or. anlorganic compiex thereof', or 'Brano catalyst in the alkylation;

zone 44. Other alkylation catalysts may be used.' The rate of throughput of the mixture over the aluminum chloride catalyst is about two volumes of hydrocarbons, calculated as cold liquid, per Volume of catalyst per hour. The reaction is carried out under a pressureof about 350 lbs/sq. in. I

The products of alkylation are passed through line |42 to a fractionating tower |44 to separate desired constituents from gas and bottoms. The

gas which consists largely of those impuritiesl present in the feed passes overhead through line |46 and the bottoms or heavy oil polymers areY withdrawn from the bottom of the tower through. line |46. Provision is made in the tower |44 to.

separate a C5 and Cs fraction and withdraw it through line |52 and a higher boiling C7 and Cs' fraction and withdrawing it through line |54.

Heavy alkylate is withdrawn from the lower portion in the tower |44 through line |56. This heavy alkylate may be used in ordinary motor The C5 and Cs fraction contains a relativelylarge amount of2`,3-dimethyl butane fromthe alkylation of ethylene and forms an exceedingly) good blending agent for aviation gasoline.

ethylene.

The fractions withdrawn through lines |52 and d |54 may be combined and directly introduced into the aviation gasoline.

Referring now to the second Yalkylation zone 64,

the feed comprises isobutane from line 58, propylene passing through line 56 from tower 52 and butanes and butylenes from the extraction step 16 passing through line 82. In the simplestV case this mixture is heated to a temperature of about F. and then contacted with a suitable alkylation catalyst, such as sulfuric acid or hydroluoric acid. Other alkylation catalysts may bev used including aluminum chloride. The rate of throughput of the mixture over thesulfuric acid is about two volumes of hydrocarbon calculated as cold liquid per volume of catalyst per hour. The reaction is carried out under a pressure of about 200 lbs/sq. in.

The productsof alkylation are passed through line |60 to a fractionating tower |62 provided with heating means |63 to separate desired con- Gas passes overhead through line |64 stituents. and bottoms, such as heavy polymers, are withdrawn from the bottom of the tower through line |66. An alkylate fraction containing mostly C5 to Cs branched chain hydrocarbons is withdrawn through line |68. Another fraction containing C9 to C12 hydrocarbons is withdrawn.

through line |12. These alkylate fractions contain isoparafnic hydrocarbons present in com-V mercially produced alkylates and are introduced directly into the aviation gasoline, kylate boiling above about 350-370 F. is withdrawn from a lower portion in the tower |62 through line |14 and forms an excellent blending agent for ordinary motor gasolines.

If desired, a portion of the benzene may be separated from the aromatic fraction passing through line |68 and this benzene passed through line |15 and mixed with propylene withdrawn through line |16 from line 56. The mixture is passed to a third alkylation zone |18 under suitable conditions to produce cumene which is with- I drawn through line |82. The cumene is intro` duced tothe aviation gasoline. This step is givenv A heavy 2.1-

7 merely as an alternative and may be omitted if desired.

While I have shown two Valkylation zones 44 and 64, it is within the contemplation of my in,- vention to use a single alkylation zone for alkylating both the ethylene and isobutane and propylenes .and isobutane. Or it maybe desirable to use separate alkylatio'n Zones for alkylating Cz, C3, C4 oleflns separately with isobutane so that .special processing conditions may be individually employed.

According to the above process, the finished aviation gasoline produced containing the above enumerated fractions is withdrawn through line 18B.

The aviation gasoline produced according to the above process is unique in its properties, in that, while it remains a true aviation gasoline as regards all specifications on boiling range, heating value, aromatics content, etc., nevertheless, it possesses more blending power in improving rich mixtures or 3C rating than do the commonly known special blending agents, such as commercial hydrocodimer or alkylates, which are very deficient in volatility-especially at the 167 F. point. It is also superior to the use of aromatics alone since these compounds (1) are generally less volatile; (2) have an adverse effect on lean mixture performance; and (3) are strictly limited in use by specification on this allowable content in the fuel.

The fuel produced by my invention has, for example, the following properties as compared -to Y hydrocodimer and butenes alkylate.

Special Hydro- Butene Fuel codimer Alkylate Distillation Characteristics:

R. v. P 5 2 3 Per cent Dist. 167... 29 0 0 Per cent Dist. 221... 70 50 50 Per cent Dist. 293 96 90 90 Octane Characteristics:

AFD-1C (+4 cc. TEL) Octane f No 107. 5 107. 5 107. 5 AFD-3C V(+4 ce. TEL) IMEP. .n 287 280 240 fuel result for each volume of the special fuel used. The amount of aviation fuel improved in thisy manner depends upon the quality of the base fuel. For example, if it is desired to improve present commercial grade 130 `aviation fuel of S+1.25 cc. of tetraethyl lead 3C rating to S|2 cc., only 23 per cent of the special fuel is required, or there results a production 430 per cent, based on the special fuel, of the Si2 cc. of tetraethyl lead quality blend. If it is desired to improve low quality virginY aviation base stock of about 91 1C to S|1.25 3C quali-ty there results a production of per cent, based on the special fuel, vof .S4-1.25 qualit-y.

The `especially superior blending properties of the fuel produced by my invention are ldue to the large amount of 2-3 dimethyl butane present in combination with aromatics, thus elevating 3C rating with none of the Vdisadvantages .0f single Severe cracking,

8 carried Aout as specified, produces v'raw materials in the precise ratio required 'to synthesize the special fuel claimed.

Referring now to Fig. '2 of the drawings, the

, reference character 210 designates a line through which virgin motor gasoline is passed and introduced into a fractionating tower l212 having la suitable heating means 213 in a lower portion thereof for supplying heat to the feed stock.

In the fractionator 212 lower boiling hydrocarbons are taken overhead through line 214 and higher boiling hydrocarbons are taken off as bottoms through line 21B. The vfraction taken overhead has an end boiling 'point-of about 250 F.

so that the fraction taken overhead contains C4 to C8 hydrocarbons. Fractionating tower 212 and all fractionating towers hereinbefore and hereinafter to be described contain means for refluxing in the tower during fractionation.

The lower boiling hydrocarbon fraction is injtroduced into fractionating tower 211i which may be called a debutanizer for removing C4 hydrocarbons from the low `boiling fraction. Fractionator 218 is provided with heating means 219 for supplying vheat to the tower. A Ci fraction is taken overhead as a vapor through line 222 and "further treatment of this fraction to produce isobutane will be hereinafter described.

The bottoms from the fractionating tower 218 are passed through line 224 to another fractionating tower 2,26 which may be referred to as a depentanizer tower for removing Cs hydrocarbons from the rest of the fraction. The C5 hydrocarbons pass overhead through line 223 as vapors and are further treated as will be hereinafter described to separate normal pentane from isopentane. Tower 226 has heating means 230.

The bottoms from the fractionating tower 226 are passed through rline 2,32 to another fraction ating tower 2,36 having heating means 238. The tower 2,36 is used to remove a Cs fraction from the higher boiling Vconstituents and the Cs fraction pasesvs overhead as a Vapor through line 242.

Bottoms from the fractionating vtower l236 are passed through line 244 to another fractionating tower 2d6 which is used to separate the lower boiling portion of 'the Ci fraction overhead from higher boiling constituents, This lighter Cv fraction .contains mostly isohe'ptane which is used as one of the Iingredients of aviation gasoline made according to my invention.

'jhge fractionating tower 246 is provided with heating means .248 for supplying heat to the tower. The isoheptane fraction is withdrawn overhead as a vapor .through line 252 and is cooled and recovered ajs .a liquid fraction which may be added to the final product. The isoheptane is about the lo'wes'tquali'ty material present, however., and in some cases it 'may be desirable to include it in the feed to the cracking unit 12 (Fig. 1) rather than including it in aviation gasoline. The higher boiling constituents are withdrawn as bottoms from the fractionating tower 2.46 through line 25,4 and are mixed with'the higher boiling fraction of the ^feed Stock withdrawn from the bottom of the @ist fractilting tower 212 through line 218.

This mixture is v.Sirr'lilar to the heavy naphtha feed used in the process described in Fig. l as it has a'boiling range of about 20G-410 F. and this mixture forms a feed which is passed through the. process .described .in .connectionwith Fig. 1 to produce aromatcsand alkylate. when usine the Fig, 2 modification, the isomerization VZone 122 in Fis. 1 may ,be omitted as .another isomerization `zone is provided in Fig. 2.

Returning now to the debutanizer tower 2`I8, the C4 hydrocarbons pass overhead through line 222 and are mixed with C4 hydrocarbons passing through line 212 from an isomerization step to be presently described and this mixture is intro- Y butane, the isobutane passing overhead' through'A line 218 and being passed as part of the isobutane to either or both alkylation zones 44 and 64 in Fig. 1.

The normal butane is withdrawn as bottoms from the tower 214 through line 284 and is heatedj and then introduced into an isomerization zone 294. Normal butane from an extraneous source is introduced into the isomerization zone 294 through line 206. Any suitable isomerization catalyst, such as aluminum chloride and an activation agent, such as hydrogen chloride, may be used in the isomerization zone 294. The temperature during isomerization is about 20G-325 F.

and the throughput of the reactants over the catalyst is about 0.5 to 1.0 volume of hydrocarbon,

taken overhead as a vapor through line 306 andl higher boiling constituents are withdrawn as botltoms through line 308 and returned to the feed line'2l0 for introduction into the iirst fractionating tower 212. The line 306 forms a continuation of line 212 above described so that the C4 fraction is introduced into the isobutane tower 214 for separating isobutane from normal butane as above described.

Returning now to the depentanizer tower 226, the C5 fraction passing overhead through line 228 is introduced into a fractionating tower 3 I 2 which is designated isopentane tower on the drawing. The fractionating tower is provided with a heating means 3l4. The tower 3I2 is adapted to separate normal pentane from isopentane. The isopentane is lower boiling and is taken overhead through line 316. The isopentane is a desirable constituent for aviation gasoline and forms one of the blending agents to be added to aviation gasoline made according to this vention.

Normal pentane is withdrawn from the bottom of the tower 312 through line 3I8 and is mixed with the C6 fraction leaving the top of tower 236 through line 242. The mixture of C5 and Cs hydrocarbons is then passed through line 322 and is further mixed `with hydrogen introduced into line 322 through line 324. About 100 to 200 standard cubic feet of hydrogen per barrel of liquid C5 and Ce hydrocarbons is used. Themixture is then passed through a heating coil 326 in a heater 328 to heat the mixture to a temperature of about 300 F. and the heated mixture is then introduced into a second isomerization zone 332 wherein the mixture is contacted with an isomerization catalyst like anhydrous aluminum chloride, a hydrocarbon complex thereof, or other well known catalysts. The hydrocarbons are contacted with the `catalyst at a throughput rate of about 1 to 3 volumes of hydrocarbon feed, calcuform of my inv lated'as cold oil, pervolume of catalyst per hour.

During isomerization of the Cs and Cs fractions, branched chain isomers are formed from the straight chain feed materials, for example, about 85 per cent of the normal pentane is converted to isopentane. The normal hexane is converted to a mixture of its branched chain isomers 2,2-dimethyl butane, methyl pentanes, etc., all of which are of improved octane rating over the feed.

The products of isomerization are withdrawn from the zone 332 through line 334 and introduced into a fractionating tower 336 provided with a heating'means 338. The relatively light Ahydrocarbons which are formed by molecular splitting side reactions'and which contain normal butane and Aisobutane and are passed overhead through line 342 in vapor form are introduced t into line 222 for introduction into isobutane tower 214 wherein normal and isobutane are separated.

The bottoms from the tower 336 contains isopentane and isohexane and are withdrawn through line 344. The mixture contains mostly branched chain C5 'and Cs hydrocarbons, isopentane, isohexane, etc., and vforms one ofthe blending agents'to be added to aviation gasoline made according to this form of my process. From the above description of the Fig. 2 modiiication, it will be seen that isoheptane and isopentane are .recovered by fractionation and may -be added directly to the aviation gasoline. The separated butane fraction is isomerized t0 form part of the isobutane feed for the alkylation Zone.

Normal pentane'and hexane are isomerized to form the iso-compounds. The heavy fraction of the feed passing through lines 216 and 254 is severely `cracked to produce aromatics, olens including ethylener and Cs and C4 olens forallkylation, and butadiene, as described in the process in connection with Fig. l using heavy naphtha.

The aviation gasoline producedbi7 the apparatusof the modification shown in Fig. 2 and supplemented by the showing in Fig. 1 is inferior to that producedl from the process described in connection withFig. 1 but produces an aviation gasoline having a S-Crating of S|3.0 cc. of tetraethyl lead and has an IMEP of 235. n

Best results are'produced by alkylating isobutane with ethylene to produce the maximum yield of 2,3-dimethy1 butane. The butylenes and propylenes from the cracking operation may be alkylated separately or jointly with isobutane to increase the yield of material suitable for use as .blending agents but such alkylates are inferior to ethyleney alkylates as blending agents for aviation gasoline. Also, forl example, the propylene may be absorbed in sulfuric acid and hydrolyzed to form isopropyl ether, which is not presently used as a blending agent in aviation gasoline but which may be used for ordinary motor fuels. This material is of excellent octane rating but has certain disadvantages which have not yet been overcome for use in aviation fuel.

For optimum results and to produce maximum butadiene, isoprene, etc., as rubber raw materials, two-stage cracking may be used. When charging heavy virgin naphtha to the cracking operation, the first stage is operated to produce maximum diolefins and the temperature of cracking is about 1300 F. to 1315 F. for a time of reaction of about 0.3 second. Heavier stocks are less refractory, for example, only1200 F. is required on virgin gas oil for the first stage tracking. After recovery of butadiene, isoprene,

piperylene, etc., the distillate from the rst stage is then recracked in a second stage under intensive conditions of at least 1375 F. and 1 second, or a time-temperature relationship of equivalent severity, to produce some incidental additional diolefin, such as butadiene, but mainly to convert the distillate material to aromatics. The liquid cracked products from the second Stage are practically 90% to 100% aroma-tics and it is relatively simple to purify these reaction products by acid-treating and fractionating as above disclosed or described.

The highest quality aviation gasoline is therefore obtained in a mixture of 2,3-dimethyl butane plus benzene, toluene and xylenes together with C3v and C4 alkylate. One advantage in product quality obtained by using the modified form of my invention for treating virgin motor gasoline or naphthas is the fact that the combination of steps gives a product which is extremely volatile, approaching 40% at .158 F. yet with only 7 lbs. R. V. P. As a result, the product can carry relatively non-volatile lower performance base stocks and bring them up to the desired specifications on both octane rating and volatility.

Starting with virgin East Texas motor gasoline and carrying out my process, a yield of about 60% of aviation gasoline is produced.` The aviation gasoline has an IMEP of about 235 with 4 cc. of lead. The-amount of butadiene produced is about 3% by Weight on the feed on single stage cracking, but may be approximately doubled Without greatly affecting yields of other products by employing two-stage cracking as outlined.

While the drastic vapor phase cracking treatment produces about 50% by Weight of gas on the feed, it will be seen that a large part of the gas formed comprises very valuable products, i. e., olens and diolens, which may bey recovered as such, or which, in the case of the olens, may be used in the alkylation step. The diolens form valuable products which are recovered as such. The cracking process therefore performs the function of taking the charge 4stock molecules apart into basic molecular groupings which may then be reassembled as desired by the subsequent processing to result in a desired product having unusual properties.

The analysis of one type of aviation gasoline blending stock which may be obtained With my process contains about (a) 40% by volume of branched chain C5, Cs, C7 and Ca hydrocarbons with this fraction comprising mostly Cv and Cs hydrocarbons,r (b) about 34% by volume of 2,3- dimethyl butane and (c) about 26% by volume of an aromatic fraction consisting essentially of benzene, toluene and Xylenes with the benzene not over about of the total blending stock. The percentages of fractions a, b, and c may be varied but according to my invention the presence of a relatively large amount of 2,3-dimethyl butane is preferred in the combination of fractions above set forth.

While I have set forth diierent forms of my process and have included specic details as to temperatures, pressures, feed compositions, etc., andone example of an aviation blending stock or fuel, it is to be understood that these are by Way of illustration only and that changes and modications may be made Without departingv from the spirit of my invention. What I claim is: 1. In a process for producing aviation gasoline blending stock, the steps which comprise severely thermally cracking in a single stage at a temperature in the range of about 1200u F. to 1400 F. a heavy naphtha in the boiling range of about 200 F. to about 410 F. to convert substantially all of the parailins and naphthenes into aromatic hydrocarbons including benzene, toluene and Xylenes admiXed with olefins containing a large amount of ethylene and some diolens, separating from the cracked products an aromatic iraction consisting essentially of aromatic hydrocarbons in the aviation gasoline boiling range and ethylene, catalytically alkylating the separated ethylene With isobutane to form a branched chain hydrocarbon fraction containing an appreciable amount of 2,3 dimethyl butane and blending at least part of the separated aromatic fraction with the alkylated branched chain hydrocarbon fraction to form aviation gasoline blending stock.

2. A method according to claim 1 wherein isobutane is separated from the heavy naphtha before the severe thermal cracking step and the separated isobutane is used in the catalytic alkylation of ethylene.

3. A method according to claim l wherein the olens in addition to ethylene contain C3 and C4. olens, the C3 and C4 oleflns are separated and catalytically alkylated with isobutane to form higher boiling branched chain hydrocarbons in the aviation gasoline boiling range and at least part of the last-mentioned hydrocarbons is blended with theA mixture of branched chain hydrocarbon fraction and aromatic fraction.

4. In a process for producing aviation gasoline blending stock, the steps Which comprise thermally cracking in a single stage a heavy virgin naphtha in the boil-ing range of about 200 F. to 410 F. at a temperature in the range of about 1200 F. to 1400 F. to convert parains and naphthenesy into aromatic hydrocarbons boiling in the aviation gasoline boiling range, said aromatic hydrocarbons comprising a fraction consisting essentially of benzene, toluene and Xylenes, ethylene, C3 and C4 olens, segregating ethylene from C3 and C4 olens, catalytically alkylating isobutane and the separated ethylene to form branched chain hydrocarbonsV in the aviation gasoline boiling range and including 2,3 dimethyl butane, separately catalytically alkylating isobutane with the separated C3 and C4 olens to produce branched chain parains in the aviation gasoline boiling range and blending the aromatic hydrocarbons with at least part of said branched chain hydrocarbons and said branched chain parailns.

5. A process of producing aviation gasoline blending material which comprises separating normal butane' and isobutane from a heavy naphtha fraction, 'catalytically isomerizing the separated normal butane to form an additional amount of isobutane which is added to the separated isobutane, thermally cracking the remaining heavy naphtha fraction in the boiling range of about 200 F. to 410 F. at a temperature in the range of 1200 F. to 1400 F. to convert paraiiins to aromatic hydrocarbons, ethylene, other olens and diolens', separating ethylene from the cracked products, catalytically alkylating said isobutane With the separated ethylene to form higher boiling branched chain hydrocarbons containing an appreciable amount of 2,3 dimethyl butane, treating the aromatic hydrocarbons to remove oleiins and dioleflns therefrom and recovering an aromatic fraction containing benzene, toluene and Xylenes and mixing the higher boiling branched chain hydrocarbons with the aromatic fraction to produce an aviation gasoline blending material.

6. A process for producing blending material for aviation gasoline which comprises fractionating a hydrocarbon oil to separate isobutane, a C fraction and a C6 fraction from a heavy naphtha, thermally cracking the resulting heavy naphtha in the boiling range of about 200 F. to 410 F. at a temperature in the range of 1200 F. to 1400" F. to produce aromatic hydrocarbons in the aviation gasoline boiling range having admiXed therewith olens including ethylene and diolens, separating ethylene and an aromatic fraction containing a major proportion of benzene and toluene from the cracked products, catalytically alkylating the separated ethylene and said isobutane to produce branched chain hydrocarbons including an appreciable amount of 2,3 dimethyl butane, catalytically isomerizing the separated C5 and Cs hydrocarbons to form iso hydrocarbons and mixing said lastmentioned iso hydrocarbons with said separated aromatic fraction and said branched chain hydrocarbons containing 2,3 dimethyl butane to form aviation gasoline blending material.

7. A process according to claim 6 wherein the thermally cracked products include isobutane, propylene and butylenes, the propylene and butylenes are separately catalytically alkylated with isobutane at least part of which is recovered from the thermally cracked products to form higher boiling branched chain hydrocarbons and fractionating the last-mentioned hydrocarbons to recover branched chain hydrocarbons in the aviation gasoline boiling range and which are mixed with said aviation gasoline blending material.

f CLARKE T. HARDING.

REFERENCES CITED The following references are of record in the file of this patent:

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